The present invention relates to a control device for an electronic timepiece, and in particular to a control device for controlling a stepping motor used in an electronic timepiece which uses kinetic energy to drive a electricity generating device to provide electronic power for driving the stepping motor.
In recent years, timing devices, such as wrist-watches, have been sold with built-in electricity generators in which the energy generated by the movement of the user""s arm is converted into electricity which is used to drive the stepping motor which moves the hands of the device. These timing devices operate without batteries and can continuously run off the energy generated by the user""s movement. Also, these timing devices eliminate the often cumbersome process of changing batteries as well as help reduce the environmental hazard associated with battery disposal. As a result, built-in electricity generators are being closely evaluated for future widespread use in wristwatches and similar devices.
Generally, electronic timepieces that incorporate electricity generators include a stepping motor for driving the hands of the timepiece. These stepping motors, also referred to as a pulse motors or digital motors, are driven by pulse signals and are also extensively used as actuators for digital control devices. In recent years, compact electronic devices and information equipment have been developed in which portability is desirable, and compact and lightweight stepping motors are in widespread use as actuators for this equipment. Representative of such electronic devices are timing devices including electronic timepieces, time switches and chronographs.
Referring now to FIG. 12, there is shown a prior art timing device 9, for example a wristwatch, which includes a stepping motor 10, a driving circuit 30 for driving stepping motor 10, a gear train 50 for transferring the force of stepping motor 10, a second hand 61, a minute hand 62, and an hour hand 63 which are moved by gear train 50. Stepping motor 10 generates magnetic force in response to driving pulses supplied from a control device 20. Stepping motor 10 includes a driving coil 11, a stator 12 which is excited by driving coil 11, and a rotor 13 which rotates within stator 12 as a result of the excited magnetic field. By selecting a disk-shaped bipolar permanent magnet for rotor 13, a PM-type (Permanent Magnet rotational) stepping motor is formed. Stator 12 is provided with a magnetism saturating unit 17 so that the different magnetic poles that result from the magnetic force generated by driving coil 11 are generated at the phases (poles) 15 and 16, respectively surrounding rotor 13. Also, an internal notching 18 is provided at the appropriate location on the inner periphery of stator 12 so that cogging torque is generated and rotor 13 is stopped at the appropriate position.
The rotation of rotor 13 of stepping motor 10 is transferred to each of the timepiece hands by gear train 50 which includes a fifth gear 51 meshing with a fourth gear 52, which also meshes with a third gear 53, which meshes with a center wheel 54. Center wheel 54 meshes with a minute wheel 55, which meshes with an hour wheel 56. Second hand 61 is connected to the axis of fourth gear 52, minute hand 62 is connected to the axis of center wheel 54, and hour hand 63 is connected to the axis of hour wheel 56. Time is displayed by each of the timepiece hands operating synchronously with the rotation of rotor 13. Of course, a transfer system for displaying the year, month, and day (not shown) may also be connected to gear train 50. In order for timing device 9 to display the time as a result of the rotation of stepping motor 10, stepping motor 10 is supplied with driving pulses which are based on counting (timing) of signals generated by a reference frequency.
Control device 20, which controls stepping motor 10, includes a pulse synthesizing circuit 22 for generating reference pulses of a standard frequency using a reference oscillator 21 such as a crystal oscillator, or pulse signals of a different pulse width or timing. The reference pulses are input to a control circuit 23 for controlling stepping motor 10 based on the various pulse signals supplied from pulse synthesizing circuit 22. Control circuit 23 has a driving control circuit 24 which receives the reference pulses for controlling driving circuit 30, and a detecting circuit 25 for detecting whether driving rotor 13 rotated. Driving control circuit 24 includes: a driving pulse supplying unit 24a for supplying driving pulses to driving circuit 30 which in turn drives driving rotor 13 of stepping motor 10; a rotation detection pulse supplying unit 24b for outputting rotation detecting pulses to detection circuit 25 for inducing induction voltage to determine whether driving rotor 13 rotated in response to the driving pulse; a magnetic detection pulse supplying unit 24c for outputting magnetic field detecting pulses to detection circuit 25 prior to the output of the driving pulse, for inducing induction voltage to detect the presence of a magnetic field external to stepping motor 10; an auxiliary pulse supplying unit 24d for generating an auxiliary pulse that has an effective electric power that is greater than that of the driving pulse, the auxiliary pulse being output if the driving pulse does not cause driving rotor 13 to rotate or if an external magnetic field has been detected; and a demagnetizing pulse supplying unit 24e for producing a demagnetizing pulse having a polarity that is opposite that of the auxiliary pulse and which is used to demagnetize driving coil 11 after the auxiliary pulse is output.
Detecting circuit 25 includes a rotating detecting unit 26 for comparing the rotation detecting induction voltage, obtained by outputting the rotation detecting pulse, with a set value, and detecting whether driving rotor 13 rotated. Detecting circuit 25 also includes a magnetic field detecting unit 27 for comparing the magnetic field detecting induction voltage, obtained by outputting the magnetic field detecting pulse, with a set value for detecting the presence of a magnetic field.
Referring now to FIG. 13, there is shown rotation detecting unit 26 which employs a pair of comparators, 29a and 29b, to compare the value of the bi-directional excitation voltage generated in driving coil 11 with a set value SV1, to determine whether driving rotor 13 has rotated. Comparator 29a receives one input from the standard signal SV1 and a second input xcfx861 from one side of driving coil 11 and produces a first comparison signal. Similarly, comparator 29b receives a first input SV1 and a second input xcfx862 from the other side of driving coil 11 and produces a second comparison signal. An OR gate 29c receives the first and second comparison signals and produces an output to driving control circuit 24. Similarly, magnetic field detecting unit 27 uses a pair of inverters, 28a and 28b, each having a threshold value of SV2, which receive the inputs of xcfx861 and xcfx862, respectively. These inverted signals are input to an OR gate 28c for detecting the presence of a magnetic field. The results of each comparison are fed back to driving control circuit 24, and are used for controlling stepping motor 10.
Driving circuit 30, which supplies various driving pulses to stepping motor 10 under the control of driving control circuit 24, coupled between driving control circuit 24 and a battery 41, has a bridge circuit which includes a serially connected p-channel MOSFET 33a and n-channel MOSFET 32b, and serially connected p-channel MOSFET 33b and n-channel MOSFET 32a, configured for controlling the voltage supplied to stepping motor 10 from battery 41. Also included are a pair of rotation detecting resistors 35a and 35b connected in parallel to the p-channel MOSFET 33a and 33b, respectively, and a pair of sampling p-channel MOSFET, 34a and 34b, coupled between ground, driving circuit 24 and resistors 35a, 35b respectively for supplying chopper pulses to resistors 34a and 35b. Control pulses having different polarities and pulse widths are output from supplying unit 24a through 24e of driving control circuit 24 to the gate electrodes of each of MOSFET 32a, 32b, 33a, 33b, 34a and 34b according to the respective timings. Thus, driving pulses having different polarities drive driving coil 11 and pulses for inducing induction voltage for rotation detection of rotor 13 and magnetic field detection are supplied.
Referring now to FIG. 14, there is shown a timing chart illustrating the control signals supplied to gates GP1, GN1, and GS1 of the p-channel MOSFET 33a, n-channel MOSFET 32a, and sampling p-channel MOSFET 34a, respectively, for excitation of a magnetic field of one polarity across driving coil 11, and to gates GP2, GN2 and GS2 of the p-channel MOSFET 33b, n-channel MOSFET 32b, and sampling p-channel MOSFET 34b, respectively, for excitation of a magnetic field of a reverse polarity across driving coil 11. Control device 20 controls the movement of the timepiece hands each second, by supplying a series of control pulses to driving circuit 30 which in turn controls stepping motor 10. At the beginning of a timing cycle, pulses SP0 and SP1 are output from driving control circuit 24 for detecting whether a magnetic field is present which causes rotation detection to be unreliable. Pulse SP0, which is output at the time t1, is used for detecting the presence of a magnetic field due to high-frequency noise. The control signals for outputting magnetic field detecting pulse SP0 are supplied by magnetic field detecting pulse supplying unit 24c to gate GP1 of the p-channel MOSFET 33a on the driving side (driving pole side) i.e. the side of driving circuit 30 from which driving pulse P1 is output. Magnetic field detecting pulse SP0 is a continuous control pulse having a pulse width of approximately 20 ms and is used to detect magnetic noise caused by, for example, the switching of household electrical appliances such as electric blankets or infrared foot-warmer tables. After pulse SP0 is output, a control signal for outputting a magnetic field detecting pulse SP1 for detecting alternating current magnetic fields of 50 to 60 Hz is output at time t2 by magnetic detecting pulse supplying unit 24c to gate GP2 of p-channel MOSFET 33b on the side that is opposite to the driving pole side (i.e. reverse pole). Magnetic field detecting pulse SP1 is an intermittent chopper pulse having a duty ratio of approximately xe2x85x9, and samples the electric current induced in driving coil 11 by the alternating current magnetic field thus enabling magnetic field detection unit 27 of detecting circuit 25 to detect the presence of a magnetic field. Also, because the magnetic field detecting capabilities of the driving side, i.e., the p-channel MOSFET 33a and the n-channel MOSFET 32a, deteriorates after an auxiliary pulse is applied, control pulse SP1 is output to gate GP2 of p-channel MOSFET 33b which is at the opposite pole of the driving side (reverse pole). Such magnetic field detection is disclosed in detail in Japanese Examined Patent Publication No. 3-45798.
After magnetic field detecting pulses SP0 and SP1 are output, control pulses for outputting driving pulse P1 at time t3 is supplied by driving pulse supplying unit 24a to gate GN1 of the n-channel MOSFET 32a and gate GP1 of the p-channel MOSFET 33a of the driving pole side. The effective electric power of the driving pulse P1 is reduced to approximately the limit of rotation of driving rotor 13, and is selected such that driving pulse P1 has pulse width of, e.g. W10. The control signal for outputting driving pulse P1 can vary the pulse width of driving pulse P1 thereby controlling the effective electric power of driving pulse P1. If driving rotor 13 does not rotate in response to driving pulse P1 and it is therefore necessary to output auxiliary pulse P2 to rotate driving rotor 13, the pulse width of driving pulse P1 is widened thereby increasing its effective electric power. On the other hand, if rotor 13 is continuously driven for a predetermined number of times by driving pulses P1 having the same pulse width, the effective electric power of driving pulse P1 can be reduced by narrowing its pulse width.
After driving pulse P1 is output, rotation detection pulse supplying unit 24b outputs a rotation detection pulse SP2 to gate GP1 of the p-channel MOSFET 33a on the driving side and to sampling p-channel MOSFET 34a at time t4 for detecting whether rotor 13 rotated. Rotation detecting pulse SP2 is a chopper pulse with a duty ration having approximately xc2xd, and causes the induction electric current induced in driving coil when rotor 13 rotates to be output to rotation detecting resister 35a. The voltage across rotation detecting resister 35a is compared by rotation detecting unit 26 of detecting circuit 25 with a set value SV1 for determining whether driving rotor 13 has rotated.
If the induction voltage induced by rotation detecting pulse SP2 is not at least set value SV1, it is determined that rotor 13 did not rotate, and a control signal for outputting auxiliary pulse P2 at time t5 is output from auxiliary pulse supplying unit 24d to gate GP1 of n-channel MOSFET 32a on the driving side and also to gate GP1 of p-channel MOSFET 33a. Auxiliary pulse P2 has a width of W20 and has a greater effective electric power than driving pulse P1. Thus, auxiliary pulse P2 has sufficient energy to ensure that rotor 13 rotates. Auxiliary pulse P2 is output instead of driving pulse P1 when the rotation of rotor 13 is not detected and when a magnetic field is detected by either of magnetic field detecting pulses SP0 and SP1. If a magnetic noise is present in the area of stepping motor 10, it is possible that rotation detecting pulse SP2 falsely detects the rotation of rotor 13 thereby causing errors in the movement of the timepiece hands. Accordingly, if a magnetic field is detected, an unnecessary auxiliary pulse P2 is output for detecting rotation, which while increasing power consumption, will prevent errors in the movement of the timepiece hands.
If auxiliary pulse P2 is output, a control pulse for outputting a demagnetizing pulse PE at time t6 is supplied by the demagnetizing pulse supplying unit 24e to gate GN2 of n-channel MOSFET 32b, which is at the reverse pole, and to gate GP2 of the p-channel MOSFET 33b. Demagnetizing pulse PE, a pulse which is of reverse polarity to auxiliary pulse P2, reduces the residual magnetic flux of driving coil 11 which is generated by the high effective electric power of auxiliary pulse P2. After demagnetizing pulse PE is output, one cycle of the rotational driving of stepping motor 10 by one step angle is completed.
One second after time t1, the next cycle of rotational driving of stepping motor 10 by one step angle starts at t11. In this cycle, MOSFET 32b, 33b, and 34b which were on the reverse side in the previous cycle now become the driving pole side. As with the previous cycle, pulse SP0 is first output at time t11 for detecting magnetic flux noise due to high-frequency noise, and then pulse SP1 is output at time t12 for detecting noise due to a low-frequency alternating current magnetic field. If magnetic noise is not detected, driving pulse P1 is output at time t13. Because auxiliary pulse P2 has been output in the previous cycle, the effective electric power of driving pulse P1 is increased, and a driving pulse P1 a width W11 (where W11 greater than W10) is output at time t13. Next, rotation detecting pulse SP2 is output at time t14, and if rotation of rotor 13 is detected, the cycle ends.
Referring now to FIG. 15, there is shown a flow chart of the above-described operation of control device 20. First, in step ST1, a timing reference pulse is counted and a one second time duration is measured. If it is determined that one second elapses, then in step ST2, a high-frequency magnetic field is detected using magnetic field detecting pulse SP0. If a high-frequency magnetic field is detected, then, in step ST7, auxiliary pulse P2 having a greater effective electric power than driving pulse P1 is output instead of the driving pulse P1, thus preventing errors in the movement of the timepiece hands from occurring due to unreliable rotation detection. If a high-frequency magnetic field is not detected, in step ST3, the presence of an alternating current magnetic field of a low-frequency is detected in steps using magnetic field detecting pulse SP1. If an alternating current magnetic field is present, then in step ST7, auxiliary pulse P2 is output thus preventing errors in the movement of the timepiece hands from occurring.
If no magnetic field is detected in any steps ST2, ST3, then in step ST4, driving pulse P1 is output and, in step ST5 it is determined whether rotor 13 has rotated by output of rotation detecting pulse SP2. If the rotation of rotor 13 is not confirmed, then in step ST7, auxiliary pulse P2 having a greater effective electric power than driving pulse P1 is output thereby ensuring that rotor 13 is rotated. After auxiliary pulse P2 is output, in step ST8, demagnetizing pulse PE is output, and in step ST10, the level of driving pulse P1 is adjusted higher (first level adjustment). If rotation was not confirmed in step ST5, using driving pulse P1 with the same effective electric power will result in the defective rotation being repeated. Accordingly, in step ST11, the cause for the defective rotation which made the output of auxiliary pulse P2 necessary is determined and, in step ST12, the output of driving pulse P1 is set to a higher voltage level to avoid repeated defective rotation in the next cycles. The system then returns to step ST1.
If, in step ST5, the rotation of rotor 13 as a result of driving pulse P1 was detected, the effective electric power of driving pulse P1 is adjusted lower in step ST6 (second level adjustment). In many cases, the effective electric power of driving pulse P1 is reduced after it is confirmed several times that rotor 13 has rotated in response to driving pulse P1. By performing such control, the power consumption of pulse P1 is reduced, and error in the movement of the timepiece hands is prevented from occurring in areas where there are magnetic fields from electric and electronic appliances. Accordingly, a timing device with high reliability and low power consumption is realized.
When an electricity generating device, which converts energy from the movement of the user into electricity, is added to the timepiece, another generator that has a similar configuration as that of stepping motor 10 is introduced. The electricity generating device includes a generating rotor that rotates within a stator, the generating rotor rotates by way of an energy transferring device, such as a rotating weight, thereby changing kinetic energy into rotational energy.
However, the magnetic flux generated by the generator also generates noise that may interfere with the rotation detection of driving rotor 13 thereby lowering the reliability and accuracy of timing device 9. The noise from the generator has a frequency approximately in the range of 200 to 300 Hz and is not easily detected by magnetic field detecting pulse SP0, which is normally designed to detect high frequency noise, or magnetic field detecting pulse SP1, which is used to detect alternating magnetic flux in the 50 to 60 Hz. Furthermore, the generator only generates electricity when the rotating weight rotates due to the user""s arm movement. Accordingly, the magnetic field generated by the generator is irregular, and often only e.g., 100 ms. Therefore, it is likely that this noise may be generated at the same time that rotation detecting pulse SP2 is being output even if pulse SP0 or pulse SP1 did not previously detect the presence of magnetic flux. Also, because half-wave rectification, which requires minimal space and is inexpensive to implement, is generally used in electronic timepieces, the magnetic noise is directional. Thus, there is no guarantee that when using the conventional detection system, the presence of magnetic noise will not cause the rotation of rotor 13 to be falsely detected. Furthermore, even if magnetic noise is detected and auxiliary pulse P2, having a greater effective electric power, is output, the magnetic detection capabilities in the same direction will deteriorate due to effects of residual magnetism.
Thus, in order to achieve a highly reliable timing device, it is necessary that control devices for stepping motors built in to timing devices along with alternating current electricity generating devices be provided so that the magnetic field generated by the generating device can be eliminated.
A control device that compensates for external magnetic fields, including magnetic fields generated by an on board electricity generating device, is provided. In order to inhibit effects of the magnetic field generated by the electricity generating device as much as possible, the detection of the alternating current magnetic field is performed not only at the reverse pole side to the driving pole side, but is also performed at the driving pole side, in order to increase the likelihood of detection of the magnetic field.
The present invention includes a control device for a stepping motor. The stepping motor includes a driving rotor that is rotatably driveable within a driving stator that includes a driving coil. The driving rotor is subjected to multipolar magnetization by electric power which is supplied via a condenser. The electric power is generated by an electricity generating device which includes an electricity generating rotor rotating within an electricity generating stator. The electricity generating device is driven by a kinetic energy transferring apparatus.
The control device includes a driving circuit for supplying driving pulses to the driving coil for driving the driving rotor. A rotation detecting pulse supplying unit supplies rotation detection pulses following the driving pulse for inducing induction voltage to detect the rotation of the driving rotor. A magnetic detection pulse supplying unit supplies magnetic field detection pulses prior to the driving pulse for inducing a magnetic field detecting induction voltage to detect the presence of a magnetic field external to the stepping motor. A detection circuit compares the rotation detecting induction voltage and magnetic field detecting induction voltage obtained by the rotation detecting pulse and magnetic field detecting pulse, respectively, with respective set values, thus detecting whether rotation of the driving rotor occurred and the presence of a magnetic field. An auxiliary pulse supplying unit supplies an auxiliary pulse of effective electric power that is greater than the driving pulse if either the driving rotor does not rotate in response to the driving pulse or when the external magnetic field has been detected. The magnetic detection pulse supplying unit supplies to the driving coil, prior to the driving pulse, a first magnetic field detection pulse and a second magnetic field detecting pulse each of different polarity for detecting magnetic fields of approximately the same frequency band.
The present invention also includes a method for controlling a stepping motor in which a driving rotor is rotatably driveable within a driving stator having a driving coil, the driving rotor having been subjected to multipolar magnetization by electric power which is stored in a condenser, the electric power being generated by an electricity generating device which includes an electricity generating rotor that rotates within an electricity generating stator, the electricity generating device being driven by a kinetic energy transferring apparatus. The control method includes a driving step in which driving pulses are supplied to the driving coil for driving the driving rotor. In a rotation detecting step, driving coil rotation detection pulses are output following the driving pulse and the induced induction voltage is compared with a first set value for detecting whether rotation occurred. In a magnetic field detecting step, magnetic field detection pulses are output to the driving coil prior to the driving pulse and the induced induction voltage is compared with a second set value for detecting the presence of a magnetic field external to the stepping motor. Magnetic field detecting pulses of different polarities are output to the driving coil in order to detect magnetic fields of approximately the same frequency band. In an auxiliary pulse supplying step, an auxiliary pulse of effective electric power greater than that of the driving pulse is supplied in the event that the driving rotor does not rotate in response to the driving pulse or when an external magnetic field has been detected.
By detecting alternating current magnetic flux on the pole opposite to the driving pole side (reverse pole) in addition to the driving pole side, there is a greater possibility that the presence of a magnetic field will be detected, even in cases where the magnetic field is being generated by the electricity generator which primarily effects the driving side of the driving coil. In conventional systems, detection of the alternating current magnetic fields on the driving side is not performed. This gives rise to the danger that a magnetic field may be present on the driving side which would result in false positive rotation detection and lead to error in the movement of the timepiece hands. However, in the present invention, the probability of detecting magnetic fields is improved by performing the detection of alternating current magnetic fields on the driving side as well as on the reverse pole side because magnetic fields may then be detected at both poles and also, the detection time is doubled. This greatly improves the reliability of timing devices especially for those that include an electricity generating device because magnetic fields can be detected with a high degree of sensitivity.
Also, considering the fact that the magnetic field generated by the electricity generating device is irregular and often as short as 100 ms in duration, it is impossible to determine at what point during the driving cycle of the stepper motor the magnetic fields will be introduced. Accordingly, it is also advantageous to supply magnetic field detecting pulses immediately following the rotation detecting pulse to determine the accuracy of the rotation detection and whether the rotation detection may have been influenced by magnetic noise. Therefore, under the present invention, a control device for a stepping motor is provided which supplies a magnetic field detecting pulse to the driving coil before the driving pulse is output and also immediately following the output of the rotation detecting pulse thereby increasing the reliability of magnetic field detection. In this way, a method of controlling the stepping motor is provided which includes a first magnetic field detecting step in which magnetic field detection pulses are output to the driving coil before the driving pulse and the induced induction voltage is compared with a second set value for detecting the presence of magnetic fields external to the stepping motor. The control method of the present invention also adds a second magnetic field detecting step in which the magnetic field detection pulse is output to the driving coil following the rotation detecting pulse and the induced voltage is compared with a second set value thereby detecting the presence of a magnetic field external to the stepping motor.
Generally, electric power from the electricity generating device is supplied to the control device of the stepping motor via a capacitor or condensor. As a result, the voltage of the driving pulses and other control signals supplied to the stepping motor changes in proportion to the charging voltage stored in the condensor. As the charging voltage increases, the signal-to-noise (S/N) ratio of the driving pulse also increases which tends to reduce magnetic field detection capabilities. Thus, according to the control device and method of the present invention, the set value for detecting the presence of a magnetic field described above is made to vary with the charging voltage. In this way, the probability of detecting a magnetic field is increased by lowering the set value when the charging voltage increases so that magnetic field detection sensitivity does not deteriorate.
In a preferred embodiment, instead of trying to detect the presence of a magnetic field generated by the electricity generating device, it is determined whether electricity is being generated by the electricity generating device and, if electricity is being generated, it is assumed that a magnetic field which would effect rotation detection is present. Accordingly, in the control device of the stepping motor of this embodiment, an auxiliary pulse is supplied by the auxiliary pulse supplying unit if it is determined that the electricity generating device is generating electricity without even detecting whether a magnetic field is present. Also, although magnetic field detection capabilities are reduced when an auxiliary pulse having a greater effective electric power than the driving pulse is supplied, this is of no consequence because the determination of whether to supply an auxiliary pulse is based on whether electricity is being generated and not on the presence of a magnetic field. Accordingly, the reliability of control device of the stepping motor is further improved.
If the device has a short-pulse supplying unit for supplying short-pulses to the driving coil which have a shorter cycle than the drive pulses, for example, fast-forward pulses or reverse pulses, it is preferable that the short-pulse supplying unit stop supplying the short-pulse when electricity is being generated in order to prevent error in the movement of the timepiece hands. In particular, the voltage of the reverse pulses (which drive the rotor in the reverse direction) may fluctuate when electricity is being generated because these pulses are combinations of a plurality of short pulses which are particularly vulnerable to noise. The voltage of the fast-forward pulses may also fluctuate because these pulses also have short cycles. Accordingly, it is preferable that reverse driving as well as fast-forward pulses be forcibly terminated during electricity generation.
If a magnetic field is detected, or if the generating device is generating electricity and auxiliary pulses have been output, there is a high possibility that a residual magnetic field may remain in the driving coil which will adversely impact rotation detection. Accordingly, in a preferred embodiment, a driving pulse having a greater effective electric power than the immediately preceding diving pulse is supplied after the auxiliary pulse is output. These higher power driving pulses which will ensure rotor rotation are supplied a certain number of times following the output of the auxiliary pulse. In this way, the need to detect whether or not rotation occurred is eliminated in this situation and error in the movement of the timepiece hands can be prevented. The effective electric power of these driving pulses can be adjusted by either varying the pulse width or voltage. In addition, by supplying a demagnetizing pulse having a different polarity than that of the auxiliary pulse for demagnetizing the driving coil following the output of the auxiliary pulse and immediately before the next driving pulse, a substantial increase in the effective voltage of the driving pulse is achieved.
As described above, a control device and a method for controlling a stepping motor is provided in which the effects of the magnetic field generated by the electricity generating device stored within the device is minimized. This result is accomplished in several ways including, but not limited to: improving the probability of detection of the magnetic field; assuming the presence of a magnetic field if the electricity generating device is generating electricity instead of trying to detect the presence of magnetic fields; and supplying a driving pulse having greater effective electric power than the previous driving pulse following the auxiliary pulse. Thus, by using a control device according to the present invention, a stepping motor that can perform movement of the timepiece hands in a stable manner and with high reliability is provided. Also, by constructing a timepiece which includes a stepping motor control device according to the present invention, a stepping motor which moves the hands on the face of the timepiece using driving pulses, a pulse synthesizing unit which outputs pulse signals of a plurality of frequencies, and an electricity generating device capable of supplying the necessary electrical power, a highly precise timepiece can be provided which may be used anytime and anywhere without the use of batteries.
Furthermore, the method of controlling a stepping motor according to the present invention can be implemented in a computer-readable medium such as in the control program of a logic circuit or a microprocessor, and is therefore not restricted to timing devices and can also be applied to various motor devices which require intermittent and highly precise hand movements.
Accordingly, it is an object of the present invention to provide a control device for controlling a stepping motor for use in a timepiece together with an alternating current electricity generating device in which the effects of external magnetic fields and, in particular, the magnetic field generated by the generating device are eliminated thereby providing a highly reliable timepiece.
It is another object of the present invention to provide a highly precise timing device with a built in electricity generating device so that the need to replace and discard batteries is eliminated.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.